Method and device for controlling gear ratio change in a transmission contained in the drive train of a motor vehicle with gears that can be shifted under power

ABSTRACT

In a parallel manual transmission, an upshifting under power is executed based upon preset operating conditions, for example with a fully depressed accelerator pedal, without an electronically controlled, load-reducing ignition retard. When shifting to a higher gear, the engine output is used for increasing the speed of the engine and for the propulsion of the vehicle, based upon the operating condition of the drive train.

CROSS-REFERENCE TO RELATED APPLICATION

This is a divisional of copending application Ser. No. 10/776,454, filedFeb. 10, 2004, which claims the benefit of German Patent Application No.103 05 515.0 filed on Feb. 11, 2003. The aforementioned priorapplications are hereby incorporated herein by reference in theirentirety.

TECHNICAL FIELD

The invention relates to a method and a device for controlling gearratio change in a transmission that is contained in the drive train of amotor vehicle, with gears that can be shifted under power. Moreprecisely, the invention relates to a method and device for upshiftingan automatically shifted parallel manual transmission that is containedin the drive train of a motor vehicle. The invention further relates toa method and device for increasing the gear ratio of a transmission thatis contained in the drive train of a motor vehicle, with gears that canbe automatically shifted without interruptions in propulsive power.

BACKGROUND

Automatic drive trains including automatic transmissions that areshifted under power and that are operated by means of actuators based onpreset programs are increasingly being used in automobiles.Transmissions of this type not only increase driving comfort but theyalso enable substantial fuel consumption savings as the amount ofdriving done at lower engine speeds is increased.

FIG. 1 shows a section of a drive train of a vehicle that is equippedwith such a transmission. A twin-clutch transmission, indicated as aunit by the number 10 and also called a parallel manual transmission,has two input shafts 12 and 14, each of which can be connected via aclutch 16 and 18, respectively, to the crankshaft 20 of an internalcombustion engine. Gear wheels are arranged on the input shafts 12 and14 and can be meshed with gear wheels that are arranged on an outputshaft 22 such that the gear wheels can shift but not rotate, in order toallow shifting to different gears. The output shaft 22 is connected, forexample, to a rear differential of the vehicle.

One actuator 24 or 26 is allocated to each clutch 16 or 18,respectively, to implement its actuation.

The actuator 26 is illustrated here in detail by way of example andincludes an electric motor 30. The output pinion gear 32 of the electricmotor 30 is equipped with internal threading that meshes with a threadedtree rod 34, which is at the same time the rod for a piston 36, whichoperates in a hydraulic cylinder 38. The hydraulic cylinder 38 isconnected via a hydraulic transmission link 40 to an actuatingmechanism, for example a release lever, of the clutch 18. To ascertainthe position of the piston 36 or the release lever of the clutch 18, asensor 42, such as an increment counter, is used to determine the angleof rotation of the output pinion gear 32. Because of the threadedengagement between the pinion gear 32 and the threaded tree rod 34, thelinear shifting of the threaded tree rod 34 can be ascertained fromchanges in the angle of rotation. In order to have a point of referencethat is referred to in the shifting of the piston 36, a detector boreprovided in the hydraulic cylinder 38 can be passed over in a knownmanner, while pressure builds up in the hydraulic transmission link 40,by an increase in torque or in the energy input of the electric motor30. As additional reference points, centers of pressure or mechanicalstops for the clutch can be approached.

The gear wheels arranged on the output shaft 22 of the twin clutchtransmission 10 are moved by means of selector forks 46, which operatein conjunction with selector fingers 48, which are arranged on ashifting shaft 50. For example, a shifting shaft 50 having a number ofselector fingers 48 may be provided, which actuates all the gear wheelsarranged on the output shaft 22, or, for example, two shifting shafts 50may be provided, which actuate the selector forks of those gear wheelsthat are allocated to one of the input shafts 12 or 14. For eachshifting shaft 50, two actuators are provided, one that rotates theshifting shaft 50 back and forth around its axle to engage gears, andanother that shifts the shifting shaft 50 in accordance with thedrawing, perpendicular to the plane of the paper, to choose betweenvarious shifting tracks.

The actuators that are allocated to a shifting shaft 50 (also indicatedby “i”) are indicated in the figure by the numbers 52 and 54. Theposition sensing can be executed as described above in reference to theelectric motor 30. In order to determine the absolute position of theshifting shaft 50 or the selector finger 48, reference points areapproached, for example mechanical stops in a selector track or shiftingtrack, or mechanical stops approached by the selector forks 46themselves.

To control the above-mentioned actuators (24, 26, 52, 54), a controlunit or control device 60 is provided, which includes a microprocessor62 with a program memory 64 and a data memory 66.

Inputs 68 to the control unit 60 are connected to various task-basedsensors or position indicators, such as a wheel speed sensor 70 fordetermining the speed of a wheel, a sensor 72 for determining theposition of an accelerator pedal 73, a position indicator 74 fordetermining the position of the selector lever of a transmissionactuating device 76, an output 77 of the transmission actuating device76, through which the actuation of various control programs, for examplea comfort driving or performance driving program, is transmitted, aspeed sensor 78 for determining the speed of the internal combustionengine, etc. It is understood that the control unit 60 may also bedesigned such that it can itself recognize driving conditions and/ordriver profiles and can activate corresponding programs, such as amountain driving program or a performance driving program.

Outputs 79 from the control unit 60 are connected to the actuators,which can be actuated by another actuator, and to a powershift element80 of the internal combustion engine.

The design and the function of the above-described arrangement, whichcan be altered in a multitude of ways, are known in the art and thuswill not be described in greater detail.

One problem with this type of automatically actuated parallel manualtransmission, or with automated manual transmissions in general, lies inthe fact that under certain conditions with an acceleration reference,it is not possible to achieve the rates that can be achieved with amanually operated manual transmission.

This is due generally to the fact that with a manually shiftedtransmission, during acceleration measurement the vehicle operatesoutside of a permissible range for individual components, for examplewith extremely high shifting forces, a “smoking” clutch, etc. Withautomated manual transmissions, this is not possible since otherwise thedanger would exist that frequent repetitions of such accelerationattempts could destroy components of the drive train.

With automated manual transmissions that are shifted with aninterruption in propulsive power, during the shifting process the enginespeed is limited by means of ignition retard, or directly in thepowershift element, as otherwise the engine would race uncontrollablyduring the shifting process.

In a vehicle having a parallel manual transmission or twin clutchtransmission there is no need for slow gear shifts or a load-reducingignition retard in order to avoid a racing of the engine during theshifting process, because the next gear in the shifting process can beselected ahead of time by engaging a gear wheel of the input shaft thatis being operated with an open clutch, with a gear wheel of the outputshaft, and by effectively engaging the gear wheel by simply switchingthe clutches 16, 18. Nevertheless, with upshifts following the end ofthe overlapping phase of the two clutches 16, and 18, a load-reducingignition retard is executed in order to lower the engine speed withoutsuperelevating the output torque to the target speed. As a result ofthis load-reducing ignition retard, the available propulsive power isnot fully utilized, causing acceleration time to be wasted.

One property of automatic transmissions consists in the fact that thesetransmissions, if necessary, automatically downshift to a lower gear ortransition to a higher gear if the propulsive power is no longersufficient to fulfill the wishes of the driver. One characteristicfeature of powershift transmissions, especially parallel manualtransmissions, but also of conventional automatic transmissions thatoperate with planetary gear sets, or CVT [continuously variabletransmission] transmissions (transmissions with continuously variablegears), is that during the transition to a higher gear the engine poweris used both to increase the engine speed and to propel the vehicle,which can have a negative effect on driving comfort.

SUMMARY

The object of the invention is to provide a solution to the problemsdiscussed above.

A first solution to the object of the invention is attained with amethod for upshifting an automatically shifted parallel manualtransmission that is contained in the drive train of a motor vehicle andthat has two parallel drive trains, each with its own clutch. Each drivearm can be activated by engaging the clutch that is allocated to it, sothat in the drive arm that is not activated a new gear can be engaged.The new gear can be activated by disengaging the one clutch and engagingthe other clutch, while an upshifting of the parallel manualtransmission is effected based upon preset operating conditions, withoutan electronically controlled load-reducing ignition retard.

In accordance with a further refinement of the process specified in theinvention a preset operating condition is transmitted by means of afully depressed accelerator pedal.

In accordance with a further implementation of the process specified inthe invention, a preset operating condition is transmitted by means ofan additionally actuated shift program.

Furthermore, a preset operating condition can be provided in that thevehicle, in the depression of the accelerator pedal beyond apredetermined degree, is held at rest by an actuation of the brakes.

For the shortest possible acceleration rates, the process isadvantageously implemented such that the disengagement of the one clutchand the engagement of the other clutch are controlled such that duringat least part of the shifting process the engine runs at a speed thatcorresponds to its highest power level.

A further solution to the object of the invention is attained with aprocess for increasing the gear ratio of a transmission that iscontained in the drive train of a motor vehicle and that can beautomatically shifted without interruption of its gear ratio propulsivepower, especially a parallel manual transmission, in which process, withan increase under power of the gear ratio of the transmission, thedivision of the engine power into one portion that is available forincreasing the speed of the engine and one portion that is available forthe propulsion of the vehicle, depending upon the operating conditionsof the drive train, is changed.

Advantageously, the portion of the engine power that is available forincreasing engine speed is expanded with an increasingly rapid actuationof the accelerator pedal.

In the case of a gear ratio increase without a change in the position ofthe accelerator pedal, the engine output is advantageously used largelyfor the propulsion of the vehicle.

In a further process for controlling a parallel manual transmission asspecified in the invention, with transmissions that are in deceleration,before they drop below a minimum vehicle speed, and before the activateddriving gear is disengaged, a starting gear is engaged.

Another solution to the object of the invention is attained with adevice for controlling the gear ratio change of a transmission containedin the drive train of a motor vehicle and having gears that can beshifted under power, which includes a transmission, actuators forchanging the gear ratio of the transmission, and a control unit that isconnected to sensors contained in the drive train of the motor vehicle,and that includes a microprocessor and access memory units, whichcontrol device controls the actuators for implementing at least one ofthe above-named processes.

Below, the invention will be described by way of example, with referenceto schematic drawings, and with additional details.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other features of the present invention will be morereadily apparent from the following detailed description and drawings ofthe illustrative embodiments of the invention wherein like referencenumbers refer to similar elements and in which:

FIG. 1 is a block diagram of sections of a conventional drive train of avehicle;

FIGS. 2 a-2 c are diagrams showing an upshifting of the transmission inFIG. 1; and

FIGS. 3 a-3 b are diagrams showing a downshifting of the transmission inFIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

On the basis of FIG. 2, a conventional upshifting of the transmission 10of FIG. 1 will first be described.

In FIG. 2 a, speeds n are illustrated over time t. The curve I indicatesthe speed of the transmission input shaft 12 or 14 that is activatedfirst in a lower gear. It is assumed that this is the input shaft 12with a closed clutch 18, wherein the vehicle is driving in second gear.The curve II indicates the speed of the input shaft 14 when the thirdgear has been engaged, which is correspondingly lower than the speed ofthe input shaft 12. With a shifting from second gear to third gear, theclutch 18 that is first closed is opened, and the clutch 16 that isfirst opened is closed, so that the speed of the crankshaft 20 of theengine (curve III) moves away from the curve I and approaches the curveII.

In FIG. 2 b, the curve A represents the first closed and then openclutch 18, the curve B represents the first open and then closed clutch16, and the curve C represents the engine torque M, in the same temporalrepresentation as the curves I through III and A, B. As is apparent, theengine torque (curve C) is taken back by means of a retarding of theignition or the powershift element 80 (FIG. 1) during the drop in enginespeed (curve III), so that the “inertial force” that is produced by thereduction in engine speed does not translate to uncomfortable,supplementary propulsion. Overall, an acceleration course in accordancewith the continuous curve b₁ shown in FIG. 2 c is achieved. Due to thehigh “inertial force” of the engine, in order to produce the mostcomfortable shifting that is possible it may be necessary to drop theengine torque M to a value below zero for a short time, wherein aportion of the inertial force or rotational energy of the engine that isreleased during the drop in speed is used to drive the engine, while theremaining portion goes to accelerating the vehicle.

For a configuration that will optimize performance, it is advantageousto eliminate the engine or torque engagement in accordance with thecurve C during upshifting. The kinetic energy that is released by thedrop in engine speed is then converted to additional acceleration, asindicated by the dashed curve b₂ in FIG. 2 c. It is understood that, dueto the speeds of the input shafts 12 and 14 of the transmission that arepreset above the gear ratios, not all of the rotational energy madeavailable by the drop in engine speed can be converted to propulsivepower, rather, a portion is converted as heat in the closing clutch. Asa result of the high load on the closing clutch and the clearlynoticeable excessive increase in acceleration, it is expedient toeliminate a load-reducing ignition retard only in certain situations inwhich maximum acceleration is required, and thus momentary excessiveincreases are acceptable or desirable.

Examples of such situations are described as follows.Performance-oriented situations, such as driving with a fully depressedaccelerator pedal (kickdown). A kickdown operation can be coupled withadditional conditions, in order for the control device 60 to implementan upshifting without a load-reducing ignition retard. Such additionalconditions may include:

1. Driving starting from a stationary position with a fully depressedaccelerator pedal (detected for example by the wheel speed sensor 70 (ora sensor designed for ascertaining the speed of the output shaft 22 ofthe transmission), wherein the suppression of a load-reducing ignitionretard may occur, for example, only during a preset time interval afterdriving has started, and/or

2. Kickdown starting with a stalled vehicle, as is customary withacceleration measurements, and/or

3. Activation of an extremely performance-oriented mode (by means ofcontrol elements that are provided on the actuating device 76 or in thecontrol panel).

When one of these intake conditions, listed by way of example, isrecognized by the control unit 60 as being fulfilled, the load-reducingignition retard is not activated during upshifting as long as thedriving situation or the current operating condition of the drive trainis detected as present. As soon as this is no longer the case, forexample the accelerator pedal is no longer in its maximum position, thetime interval has expired, and/or the program is no longer selected,then the system transitions to the normal shifting process control, inwhich a load-reducing ignition retard is required during upshifting forreasons of comfort and lifespan extension.

The described suppression of a load-reducing ignition retard duringupshifting with clear reductions in engine speed can be used in alltypes of transmissions that are shifted to lower gears under power, forexample conventional automatic transmissions having planetary gear setscontrolled via clutches, CVT transmissions (such as pulley belttransmissions), etc. For the greatest possible acceleration it can beexpedient to control the clutches during the shifting process such thatthe engine (when the accelerator pedal is fully depressed) races at thehighest output speed, and then is slowed by the drag of the clutch tothe new speed.

On the basis of FIG. 3, the downshifting of the transmission 10 of FIG.1 will be described in detail below. The curves of FIG. 3 a show theengine speed n as a function of time, the curves in FIG. 3 b show theacceleration b as a function of time.

It is assumed that the vehicle is driving in a higher gear at the speedn₁, which, for example, does not increase even if the driver gives itmore gas, so that the control unit 60 controls the shifting of thetransmission to a lower gear, wherein the speed n₁ transitions to ahigher speed n₂. The continuous curve shows a relatively rapid increasein the engine speed n from n₁ to n₂. For this rapid increase in speed, agreater share of engine output, more or less depending upon the givenposition of the accelerator pedal, is required, which then is notavailable for the propulsion of the vehicle, so that the acceleration bfirst drops down, and then, once the engine is at its higher speed,assumes the constant greater value b₂. Due to the drop in acceleration,the described downshifting process is relatively uncomfortable, howeverit then leads to a rapid increase in acceleration.

The downshifting process becomes more comfortable when the speed n₁increases at a lower gradient to the speed n₂. A larger amount of engineoutput relative to the above-described case is then available for theacceleration of the vehicle, so that the acceleration b₁ drops less, andmore or less consistently approaches the higher value b₂.

According to the invention, the downshifting process is controlled bythe control unit 60, based upon the operating parameters of the drivetrain, such that the output that is available during the increase inengine speed is appropriately applied to increasing the speed of theengine itself and the acceleration or propulsive power of the vehicle.

For example, with a more rapid actuation of the accelerator pedal or ahigh pedal gradient, it is expedient to utilize a larger share of engineoutput for increasing the speed of the engine itself, in order that thehigher speed and thus the higher engine output can be realized asrapidly as possible, even if this is associated with a loss in comfortas a result of the brief reduction in propulsive power. The division ofengine output into power for accelerating the engine itself and powerfor accelerating the vehicle is accomplished by means of a coordinatedactuation of the clutches 16 and 18 (FIG. 1), wherein especially a rapidengagement of the clutch to be engaged leads to a speed course thatcorresponds to the continuous curve, and a slow engagement leads to aspeed course that corresponds to the dashed curve.

It is understood that the various types of paired clutch actuations,together with a control of the powershift element 80 by the controlunit, are possible, including, for example, a type of control in which arapid depression of the gas pedal also causes the powershift element 80to be opened during downshifting, in order to make additionalaccelerative power available to the engine itself. This can alsodefinitely result in an excessive increase in the speed beyond n₂, whichthen leads to an acceleration that lies briefly above the accelerationb₂.

If, due to a change in external conditions, for example greater drivingresistance due to an uphill grade or a strong crosswind, a lower gear iscalled for via a change to a different characteristic map while theaccelerator remains in a constant position, the driver expects a smoothshifting process, so that only a small share of output is utilized forthe acceleration of the engine, i.e. the closing clutch closes with anappropriate amount of drag.

The distribution of power during shifting can be changed not only instages, for example based upon a selected driving program (mountaindriving program, performance driving program, etc.), but alsocontinuously. This makes sense especially when the actual shiftingguidelines are continuously being shifted, for example based upon adetected uphill grade of the road, a strong crosswind, the weight of thevehicle, or a level of performance based upon the driver's behavior.These and other variables, alone or in combination, can determine thedistribution of output by means of suitable links.

If a continuous input variable for the variation of the powerdistribution is used, then the power distribution can be continuously ornon-continuously varied, based upon any function.

The described varied distribution of engine output to the accelerativepower for increasing engine speed and for the acceleration of thevehicle can be utilized in powershift transmissions of the widestvariety of constructions, such as parallel manual transmissions,conventional automatic transmissions with planetary gears, ortransmissions with continuously variable gear ratios.

One problem that occurs from time to time with parallel manualtransmissions consists in the fact that when the vehicle is stopped, orshortly before the vehicle is stopped, jolts that negatively affectdriving comfort are detectable at lower speeds. Such jolts can beprevented by preselecting or engaging the first or starting gear in theparallel manual transmission being decelerated, i.e. when the engine isbeing driven by the vehicle, below a specific minimum speed, before theclutch of the engaged driving gear, in general the second gear, opens.The preset speed can be selected, for example, such that it is the speedat which the vehicle accelerates better in first gear than in secondgear. With the timely preselection or shifting of the first gear, theengagement of the first gear that takes place with a synchronization,cannot have a disruptive effect on the still coupled shaft of the secondgear.

The following patent claims are proposed formulations, without prejudiceto obtaining further patent protection. The applicant reserves the rightto claim additional combinations of characterizing features that havebeen disclosed only in the description and/or the drawings. Referencesused in the sub-claims refer to the further development of the object ofthe main claim through the characterizing features of that sub-claim;they are not to be understood as a waiver to obtaining independentprotection for the combination of characterizing features contained inthe sub-claims. Because the objects of the sub-claims can representobjective and independent inventions on the priority date with respectto the state of the art, the applicant reserves the right to make themthe object of independent claims or declarations of division. They mayalso contain independent inventions, the form of which is independentfrom the objects of the preceding sub-claims.

The exemplary embodiments are not to be understood as a restriction ofthe invention. Rather, within the scope of the present disclosure,numerous changes and modifications are possible, especially suchvariants, elements, and combinations that, for example, can be arrivedat by an expert in the field by modifying individual features orelements or process steps described in connection with those of thegeneral description and embodiments, and the claims, and contained inthe drawings, with respect to the attainment of the object or theachievement of advantages, and that lead to a new object or to newprocess steps or process sequences as a result of combinablecharacterizing features.

1. A method for downshifting of an automatically-shifted parallel manualtransmission in a vehicle by one gear step, gears of the transmissionare changed without interruption in propulsive power, and which iscontained in a drive train of a motor vehicle, the method comprising thestep of: changing the division of engine output into one portion that isavailable for increasing the speed of the engine and another portionthat is available for the propulsion of the vehicle with an increase inthe gear ratio of the transmission under power as a result ofdownshifting by one gear step, based upon the operating conditions ofthe drive train, whereby the division of engine output into power forpropulsion of the vehicle is accomplished by means of a coordinatedactuation of dual clutches of the automatically-shifted manualtransmission.
 2. The method pursuant to claim 1, further comprising thestep of expanding the portion of the engine output that is available forincreasing the speed of the engine with an increasingly rapid actuationof an accelerator pedal.
 3. The method pursuant to claim 2, furthercomprising the step of using the engine output for the propulsion of thevehicle with an increase in gear ratio without a change in the positionof the accelerator pedal.
 4. The method for controlling anautomatically-shifted parallel manual transmission in a vehicleaccording to the method of claim 1, the method further comprising thesteps of: engaging a starting gear when the transmission isdecelerating, before the vehicle drops below a minimum speed and beforea disengagement of an activated driving gear and during an upshiftingprocess, and dividing an engine's increased torque into two parts, onegoverning propulsion of the vehicle, the other being used to acceleratethe engine's crankshaft, whereby the division of the engine's increasedtorque into power for propulsion of the vehicle is accomplished by meansof a coordinated actuation of dual clutches that are part of theautomatically-shifted parallel manual transmission.
 5. The methodaccording to claim 1, wherein the coordinated actuation of the dualclutches of the automatically-shifted manual transmission isaccomplished in one gear step.